Linear LED modules are known from the related art, in which LEDs are arranged linearly in a row in a housing having a light exit side. To be able to no longer perceive the LEDs as individual light sources and to implement the greatest possible homogeneity of the emitted light with regard to the brightness and the light color, a light-scattering matrix material can be introduced into the housing, by the light mixing and scattering effects of which more homogeneous emission of the light is enabled. To achieve satisfactory light mixing of the individual LEDs, the thickness of the matrix material, i.e., the distance from a light exit side of the LED up to the light exit side of the LED module, must be correspondingly large, in particular, this thickness must be greater, the greater the distance of the LEDs from one another is. It is disadvantageous in this case that if a volume-scattering means is used, such as the scattering matrix material, for homogenizing the light, large light losses occur, which reduces the light decoupling efficiency. This effect is greater the thicker the scattering matrix material is. To reduce the light losses due to the thick scattering matrix material, firstly a transparent layer can be provided as the matrix material, on the surface of which a thinner scattering layer is applied. Less light loss due to the scattering layer is then registered, but other problems occur in the case of this embodiment. In particular, phase boundaries between the layers result due to this two-layer or multilayer structure, inter alia, caused by adhesive layers located between the layers for fixing the individual layers on one another, on which the light is reflected.
Furthermore, the production methods for such LED modules are very complex and costly, since surface pre-treatments, for example, targeted plasma surface pre-treatments, are necessary for applying the individual layers to one another, in order to achieve sufficient adhesion of the scattering layer on the transparent layer. In particular, it must be ensured by methods having very complex production that delaminations do not form between the layers, which result in additional boundary layers in the beam path of the LED, which can be easily recognized in a linear product as clearly perceptible local light color differences.
Nonetheless, local delaminations occur between the layers in the course of time due to stresses, such as differing thermal expansion of the layers, which in turn result in increased reflection of the light and cause color variations along the linear module. Therefore, heretofore satisfactory decoupling efficiency and homogeneity of the emitted light has not been able to be achieved even by this multilayer arrangement.
FIG. 1 schematically shows a multilayer LED module 10 according to the related art in cross section to illustrate these problems. The LED module 10 includes a housing 11 in this case, in particular implemented as a U-profile, and an LED 13, which is arranged on a base side 12 of the housing 11, on a circuit board 14. Furthermore, a transparent matrix material 15 is introduced into the housing 11, on which a scattering layer 16 is arranged. The arrows shown are to schematically illustrate the light emitted from the LED 13 in this case. This LED module 10 has the disadvantage that strong reflection of the light emitted from the LED 13 occurs due to phase boundaries between the layers 15 and 16. These phase boundaries are caused, inter alia, by different refraction properties of the transparent layer 15 and the scattering layer 16, and also by adhesive layers located in between. Furthermore, local delaminations contribute to this due to stresses of the LED module 10, which also strengthen this effect of strong reflection and additionally cause color variations along the LED module 10.